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What is so special about LASER light? How do lasers work? This programme attempts to answer these questions in terms of the physical transitions (changes) of the energy states of the atoms of the l...asing material and the optical geometry of the laser itself. The programme opens with some brief examples of the wide range of applications of lasers mainly using the high localised intensity of the light. A Helium-Neon gas laser (used as part of the student home-kit for ST291 "Images and Information") is used to demonstrate the high degree of directionality and spectral purity of the light. The process of absorption, spontaneous and stimulated emission is then discussed using animated graphics and this leads to the fundamental mechanism of the LASER, namely - Light Amplification by the Stimulated Emission of Radiation. A modern high power pulsed RUBY laser is then demonstrated in a sequence recorded in the Open University physics research laboratories. The source of energy required to make the RUBY laser is in this case a high intensity 'white light' flash tube mounted in an optical cavity adjacent to the ruby rod. When this is "fired", the light emitted is focused on the ruby rod and this has the effect of "pumping" the Chronium ions in the ruby to higher "excited" energy states. Subsequently they are stimulated by a single photon to make a transition back down to a lower energy state in the process emitting a burst of identical photons - the laser output. Animated graphics are used to explain why it is that the RUBY laser emits pulses of coherent radiation, whereas the Helium-Neon gas mixture laser produces continuous coherent radiation, although at much lower power levels. In both cases energy has to be provided to cause the "population inversion" of atoms in higher energy states. This is an essential first requirement for any laser. Specially commissioned computer graphics are then used to explain why lasers tend to be long and thin. Mirrors placed with great accuracy at each end of the active medium of the laser cause the coherent radiation to be emitted at high intensity in a very fine beam. Finally we visit the research laboratory to investigate the pulse of laser light itself. The technique called "Q-switching", which enormously enhances the power of the laser pulse is dramatically demonstrated. Now, when the laser is fired a miniature ball of lightning is produced in mid air!
Metadata describing this Open University video programme
Module code and title: S271, Discovering physics
Item code: S271; 15
First transmission date: 15-09-1982
Published: 1982
Rights Statement:
Restrictions on use:
Duration: 00:25:00
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Producer: Tony Jolly
Contributors: Graham Farmelo; Keith Hodgkinson
Publisher: BBC Open University
Keyword(s): Animation; Computer graphics; Gas laser; Lightning ball; Q-switching; Ruby laser; Use of helium-neon
Master spool number: HOU4261
Production number: FOUS252X
Videofinder number: 1794
Available to public: no